Ultraviolet A (320-380 nm) radiation causes an alteration in the binding of a specific protein/protein complex to a short region of the promoter of the human heme oxygenase 1 gene.

Ultraviolet A (320-380 nm) radiation strongly stimulates expression of the human heme oxygenase 1 gene as a consequence of an enhancement in transcription rate (1). We have used a 147 bp fragment of the promoter of this gene as a probe for DNA binding activity in nuclear extracts prepared from untreated and UVA treated populations of cultured human skin fibroblasts. Analysis using gel electrophoresis mobility shift assays clearly demonstrates the appearance of a strong binding activity unique to UVA-treated extracts that is formed in the absence of de novo protein synthesis. Footprint analysis defines a binding region from -41 to -50 bp that partially overlaps with a region known to constitutively bind upstream stimulatory factor (USF). Further analysis using synthetic oligonucleotides and gel retardation has confirmed that the crucial sequence for binding the protein present in both control and UVA-treated extracts lies within a 26 bp sequence that includes the core USF binding site. UVA radiation appears to lead to a modification of the USF complex (or closely related proteins(s)) to give a structurally modified protein/protein complex which protects only the upstream half of a region originally defined by foot-printing of the promoter with USF.